Implantable infusions systems have been used to treat a variety of diseases, such as spasticity, pain and cancer by targeting drug delivery to a selected area of a patient. Therapies employing such systems have proven to be very helpful for patients for whom systemic therapy is not effective, possible, or practicable. The implantable systems typically include an implantable infusion device containing a reservoir for housing the drug and a catheter coupled to the reservoir to direct the drug to the target area. The devices typically include a pump or mechanism for driving fluid from the reservoir, or withdrawing fluid from the reservoir, and through the catheter to the selected area of the patient.
While perhaps the least complex component of an infusion system, catheters can have or can develop operational problems. For example, catheters may be placed in the wrong location when originally deployed, or the catheters may migrate over time such that drug-containing fluids delivered through the catheters are not delivered to the desired internal delivery site. Catheters can also become obstructed or clogged during use. A partial or complete blockage can prevent the drug-containing fluid from reaching the selected delivery site in an amount to be therapeutically effective. Catheters can also contain leaks, cuts, tears or the like, or can become dislodged from the infusion device, causing some or all of the drug-containing fluid to reach a site other than the intended delivery site.
Some infusion devices have been proposed that are capable of monitoring catheter complications, such as a leak, a dislodgement, a migration, or an occlusion. Many of these proposed infusion systems employ pressure sensors capable of monitoring pressure within the catheter to determine whether a complication or malfunction exists. Upon detection of a catheter malfunction or the likelihood of such a malfunction, the device may alert the patient to seek medical attention.
Methods and devices that use changes in physiological pressure to determine whether a catheter complication exists have recently been proposed. These methods and devices are based on the finding that physiological pressure changes can cause pressure modulations within an implanted catheter, provided that at least a portion of the catheter is placed in a fluid-filled space of the body that experiences the physiological pressures. For example, physiological pressure changes due to beating of the heart or patient breathing may be transduced through normally functioning catheters having at least a portion residing in cerebrospinal fluid (CSF). If the catheter migrates from the CSF, becomes dislodged, or develops a leak or tear at a location outside the CSF, a characteristic pressure profile associated with the physiological activity (e.g., heart beat or respiration) is not detected by a pressure sensor in communication with the catheter (and associated circuitry), and a catheter complication is determined to exist.
However, implementation of such methods in implantable infusion devices presents a number of challenges. First, development and detection of a full physiological pressure profile can require a good deal of sensing and processing power, which is not desired for an implantable infusion device with a limited power supply. However, limiting the acquisition or processing of data associated with the physiological pressure profiles may compromise the ability to detect catheter complications. Second, such physiological pressure profiles can be difficult to detect in the presence of background noise. For example, the amplitude of physiological pressure signals associated with heart beat or respiration within the CSF, and thus transmittable via a catheter positioned in the CSF, are quite small relative to pressure changes associated with patient activity. One or more of these and other challenges are addressed in one or more embodiments described herein.